After reading the tweet, Brown fired his agent, Brian Overstreet, claiming Overstreet said he would not be penalized if he skipped the workouts.

"He found out via Twitter that $2 million of the $2.925 million he was expecting to earn for the 2013 season had been added to the 49ers salary cap space," CEO of EAG Sports Management Denise White, acting as Brown's spokeswoman, told ABCNews.com. "It wasn't anything [Brown] was aware of. He had no idea. He was told by his agent he would be OK."

ABCNews.com reached out to Overstreet's sports agency, but did not receive a response.

Brown had spoken to his former agent "quite often" and didn't know he was supposed to attend the offseason workout, White told ABCNews.com.

"He is obviously extremely upset because he has worked extremely hard this offseason," White said. "He's worth every bit of that $2.9 million."

Brown told ABC News Radio he was unaware of the clause in his contract that indicates he needed to attend the offseason workouts. He said that agents get paid to inform players about workouts, but his agent didn't do that.

Brown felt like his body broke down in 49ers offseason workouts, White added, and wanted to train at home in Texas because he felt it better prepared him for the season.

Despite the voided $2 million from his salary, Brown is currently in 49ers training camp, White said.

Brown has played for the 49ers for six seasons and has been a starting cornerback since 2011. The 2013 NFL season, with the preseason beginning Aug. 8, marks the last year of Brown's contract and could leave him without an agent to recover his loss.

White said the decrease in $2 million is weighing heavily on Brown's mind.

"He has a great work ethic," she said. "But this is in the back of his mind and he has to get through it and have a great training camp. He is a smart a guy, a great player and will follow protocol and follow the rules."